Programmed cell death (PCD) or apoptosis is a highly regulated physiological process which eliminates specific cells from an organism. PCD plays a critical role during embryonic development but is present throughout life. Caloric restriction (CR) prolongs life span in mice by preventing age-associated disorders such as immune deficiency, malignancy, and renal disease. The precise immunological mechanisms by which CR prevents age-related deterioration of immune function are unknown. CR delays the loss of naive T cells in long-loved C57BL/6xDBA/2F1 (BDF1) mice and maintains elevated dexamethasone-induced PCD. CR also decreases breast cancer incidence in transgenic MMTV/V-Ha-ras mice by increasing the expression of p53 (apoptosis promoting) tumor suppressor gene. Others have shown that CR decreases tumorigenesis by increasing PCD in the liver. The proposed hypothesis is that CR increases negative selection and PCD in the thymus by maintaining higher circulating levels of adrenocorticoids. Further CR increases CD28 co-stimulatory interaction. This interaction promotes T cell receptor (TCR)/CD3- mediated increased differentiation and proliferation, and enhances cytotoxic T cell function. In contrast,, deficient co-stimulatory molecules in ad libitum (AL) lymphocytes may lead to accumulation of memory T cells which activate B cells. Diurnal variation and gender based differences in glucocorticoids may modulate glucocorticoid receptor (GCR) mediated PCD in lymphocyte subsets. This proposal will study PCD in immune cells from long-lived BDF1 AL and CR-fed animals to establish gender-and age-related changes. The following studies will be undertaken: 1) determine if diurnally altered GCR in CR mice parallels increased dexamethasone-induced PCD; 2) establish if there is decreased basal and TCR/CD3-induced PCD of lymphocyte subsets due to increased interaction of co- stimulatory molecules 3) determine anti-and pro-PCD gene expression in steady-state and activated T lymphocytes from CR and AL-fed young and old animals; and 4) establish if CR enhances PCD and increases life span in bcl-2 transgenic mice. In summary, to promote our understanding of immune dysfunction during aging, these studies will establish whether or not PCD of immune cells is influenced by sex-and caloric-intake.